agent: Also evict cached items via a timer.

* agent/cache.c (agent_cache_housekeeping): New func.
* agent/gpg-agent.c (handle_tick): Call it.
--

This change mitigates the risk of having cached items in a post mortem
dump.

GnuPG-bug-id: 3829
Signed-off-by: Werner Koch <wk@gnupg.org>

agent/agent.h

@@ -450,6 +450,7 @@ int agent_clear_passphrase (ctrl_t ctrl,
 /*-- cache.c --*/
 void initialize_module_cache (void);
 void deinitialize_module_cache (void);
+void agent_cache_housekeeping (void);
 void agent_flush_cache (void);
 int agent_put_cache (const char *key, cache_mode_t cache_mode,
                      const char *data, int ttl);

agent/cache.c

@@ -258,6 +258,26 @@ housekeeping (void)
 }
 
 
+void
+agent_cache_housekeeping (void)
+{
+  int res;
+
+  if (DBG_CACHE)
+    log_debug ("agent_cache_housekeeping\n");
+
+  res = npth_mutex_lock (&cache_lock);
+  if (res)
+    log_fatal ("failed to acquire cache mutex: %s\n", strerror (res));
+
+  housekeeping ();
+
+  res = npth_mutex_unlock (&cache_lock);
+  if (res)
+    log_fatal ("failed to release cache mutex: %s\n", strerror (res));
+}
+
+
 void
 agent_flush_cache (void)
 {

agent/gpg-agent.c

@@ -2398,6 +2398,9 @@ handle_tick (void)
     }
 #endif
 
+  /* Need to check for expired cache entries.  */
+  agent_cache_housekeeping ();
+
   /* Check whether the homedir is still available.  */
   if (!shutdown_pending
       && (!have_homedir_inotify || !reliable_homedir_inotify)

doc/gpg-agent.texi

@@ -403,7 +403,10 @@ control this behavior but this command line option takes precedence.
 Set the time a cache entry is valid to @var{n} seconds.  The default
 is 600 seconds.  Each time a cache entry is accessed, the entry's
 timer is reset.  To set an entry's maximum lifetime, use
-@command{max-cache-ttl}.
+@command{max-cache-ttl}.  Note that a cached passphrase may not
+evicted immediately from memory if no client requests a cache
+operation.  This is due to an internal housekeeping function which is
+only run every few seconds.
 
 @item --default-cache-ttl-ssh @var{n}
 @opindex default-cache-ttl